1. Field of the Invention
The present invention relates to a consumable guide tube used in welding. More particularly the guide tube of the present invention provides an economical and cost effective solution for guide tube manufacturing.
2. Background Art
Generally, the electroslag method generally involves bringing the ends of two substrates or workpieces together to create a gap between the ends of the plates. Welding shoes, which are generally made of copper, are then placed on each side of the gap to form a cavity between the plates and welding shoes. A steel guide tube is placed into the welding cavity for feeding a single welding wire into the cavity.
Current is then conducted through an electrode, comprising the guide tube and the welding wire, to the parent substrate material and an arc is struck in the bottom of the welding cavity. A granular flux is sprinkled into the welding cavity and melts under the influence of the arc to form a molten slag. As wire continues to feed into the cavity, the level of the molten slag rises to come in contact with the bottom of the guide tube and the welding arc is extinguished. The electric current passing between the electrode and the substrates is conducted though the molten slag. Heat generated by the molten slag melts the electrode, welding wire, and substrates to generate a molten metal puddle. Since the molten metal is heavier than the molten slag, the metal gravitates to the bottom and the slag floats on top. During the welding process current and voltage are transmitted to the molten slag and metal weld puddle. A relatively deep weld metal puddle is generated, which includes a relatively high percentage of parent material. As the weld progresses vertically, the bottom of the metal puddle cools and fuses the substrates to form an electroslag weld.
Welding wire is continually fed into the molten slag, and the weld continues to progress vertically until the welding cavity is filled with molten metal. As the weld rises, the molten slag pool continues to melt-off of the bottom of the guide tube. The guide tube is consumable and contributes to the weld metal. The copper shoes retain the molten slag and weld metal, and are removed when the weld is completed. A comprehensive description of electroslag welding is provided in the American Welding Society Welding Handbook, eighth edition, which is incorporated by reference.
A recent improvement to the traditional electroslag method has been developed by the Oregon Graduate Institute (OGI) and is known as the Narrow Gap Improvement electroslag welding method (NGI-ESW). OGI's NGI-ESW process advocates employing a narrow gap of approximately 0.75 of an inch between the substrates. Traditionally, a 1¼ inch gap between the substrates was used. Much like the previously described electroslag process, OGI advocates using a traditional guide tube design which feeds only a single wire and which does not oscillate.
Referring to FIG. 1a, a traditional winged guide tube 10 having a standard piece of heavy-wall metal tubing with wings 12. The wings 12 are separately welded to the heavy-wall metal tubing 13. The internal diameter of the metal tubing 13 is approximately ⅛ of an inch and the outer diameter is approximately ⅜ of an inch. The wings 12 are tack-welded 14 to the edges of the metal tubing as shown in FIG. 1a. 
Referring to FIG. 1b, there is shown a cross-sectinal view of the winged guide tube 10 of FIG 1a. For illustrative purposes the tack welds 14 for the winged guide tube 10 are shown.
The wings 10 are used to spread the current across the molten slag. During the welding process, the weld puddle generated by OGI NGI-ESW electroslag method is deep and wide. This deep and wide weld puddle has a high percentage of substrate metal in the weld metal. Therefore, the limitation of OGI's NGI-ESW method is that it fails to maintain a shallow weld puddle at higher welding currents. If a single welding wire is used, the puddle becomes deeper with the increase in weld speed. If the puddle becomes too deep, the grain formation creates by the solidifying weld metal can make the resulting weld more crack sensitive.
Referring to FIG. 1c, there is shown a cross sectional view of a webbed guide tube which has a plate 20 welded between a first metal tubing 22 and second metal tubing 23.
Referring to FIG. 1d there is shown a combination winged and webbed guide tube 25 having wings 26 and 27 welded to metal tubing 28a and 28b, respectively. Additionally webs 29a and 29b are welded to tubing 30 and metal tubing 28a and 28b. 
Referring to FIG. 1e, there is shown another guide tube 32 described in Canadian Patent 886,174 issued to Norcross and titled Electroslag Welding Nozzle and Process. The Norcross '174 patent describes an upwardly extending stationary consumable metallic nozzle having a metallic guide tube through which a single welding wire is introduced. The consumable metallic nozzle has wing bars extending out on two sides of the guide tube and an adhering coating of flux covering the nozzle, which melts off as the weld rises, and as the nozzle itself melts off. In an electroslag process using a narrow welding gap, i.e. NGI-ESW, the thin layer of flux used by Norcross would generate an arc between the guide tube electrode and the substrate or welding shoes. Furthermore, it the thick plates used by Norcross would draw too much amperage.
The drawback of the current design of guide tubes is that they must be custom designed for a particular application. This customization makes the guide tubes expensive to manufacture. More specifically, tubing must be purchased, and the plates must be sheared or the plates must be individually purchased. Then the plates must be welded to the tubing to meet relatively high tolerances. These guide tubes are very time consuming and expensive to manufacture.
Another drawback of the present guide tube designs is that they restrict themselves to using guide tubes which are “wedged” in place and do not oscillate. Even though multiple wire guide tube designs are taught, these guide tubes are made from tubing with wings and webs to join them together. In each case the guide tubes are “wedged” in tightly and are not configured to oscillate. Therefore, there is a need for a guide tube design which facilitates oscillation.
A final drawback to present welding methods employing a consumable guide tube is that they fail to maintain a shallow weld puddle at higher welding currents, and become crack sensitive at higher weld speeds (vertical rate of rise). When using a fixed guide tube, welding voltage must be increased to increase the diameter of the weld. To make sure that the weld penetrates all four corners of the weld cavity, the voltage must be substantially increased. This causes wider weld puddles, more substrate dilution, and larger heat affected zone (HAZ) in the substrate. This large HAZ lowers the physical characteristics of the substrate. Oscillation is used to spreads the weld puddle, instead of voltage. This results in a much smaller weld puddle, and HAZ, and better physical characteristics of the substrate with the oscillating multiwire guide tube.
Therefore, it would be beneficial to provide a standard off-the-shelf guide tube that can be used to perform a variety of welds.
It would also be beneficial to provide a consumable guide tube that is simple and economical to manufacture.
Additionally, it would be beneficial to provide a consumable guide tube which can feed at least two welding wires.
Furthermore it would be beneficial to provide a guide tube that operates in electroslag process that uses oscillation.
Further still it would be beneficial to provide a guide tube with insulator modules which prevent arcing with the substrates and the welding shoes.
Further still, it would be beneficial to provide a guide tube with insulator modules which do not increase the depth of the molten slag.
Finally, it would be beneficial to provide a consumable guide tube that can sustain a shallow weld puddle so that the resulting weld is less crack prone and impact values for the weld are increased.